The present specification relates to displays. More particularly, the present specification relates to head up displays (HUDs).
HUDs provide significant safety and operational benefits including precise energy management and conformal flight paths. These safety and operational benefits are enjoyed by operators of air transport aircraft, military aircraft, regional aircraft and high end business jets where HUD are generally employed. These safety and operational benefits are also desirable in smaller aircraft.
Conventional HUDs are generally large, expensive and difficult to fit into smaller aircraft, such as, business and regional jets as well as general aviation airplanes. Often, conventional HUDs rely on large optical components to form adequate field of view and viewing eye box. The large optical components are often associated with collimating or non-collimating projectors and include lens, prisms, mirrors, etc. The volume of the packages including the optical components of the HUD are too large to fit within the constrained space in the cockpit of smaller aircraft. Further, conventional HUDs rely upon optical components which are generally too expensive for the cost requirements of smaller aircraft.
Substrate guided HUDs have been proposed which use waveguide technology with diffraction gratings to preserve eye box size while reducing size of the HUD. U.S. Pat. No. 4,309,070 issued St. Leger Searle and U.S. Pat. No. 4,711,512 issued to Upatnieks disclose substrate waveguide HUDS. However, such systems have faced difficulties in design.
Therefore, there is a need for a compact HUD for small aircraft, such as small business jets. Further, there is a need for a compact HUD which uses collimating optics optimized for constrained spaces associated with smaller aircraft. Yet further still, there is also a need for a small volume, lightweight, lower cost collimating optics. Yet further, there is a need for a low parts count collimating system for a substrate waveguide HUD. Still further, there is a need for collimating optics with a short focal length and a low F ratio.